The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods and structures to form bandgap regulators. Typically these bandgap regulators utilized two dissimilar sized bipolar transistors as the basis of the bandgap regulator. Typically, a resistor was connected in series between the emitter of the larger transistor and the power source. The voltage developed across the resistor, and amplified by the ratio of the resistors, was utilized as a part of the stable bandgap reference voltage. In some applications it was desirable to have low power dissipation thus, the bandgap regulator was operated at low current levels, such as currents of less than two (2) micro-amps. At low current levels offset voltages developed at the input of the amplifier used to amplify the voltage across the resistor. These offset voltages resulted in an inaccurate reference voltage. Typically these offsets resulted in an error of at least approximately plus or minus four percent (4%).
At these low current levels, leakage current of the devices became a larger percentage of the current flow through the bipolar transistors and added to the inaccuracy of the reference voltage. These leakage currents typically resulted in an additional inaccuracy of up to approximately one or two percent (1%-2%).
Additionally, the low current operation also degraded the power supply rejection ratio (PSRR) of these bandgap regulators. At low currents, the pole of the PSRR of the bandgap regulator moved to lower frequencies and resulted in a more noisy output voltage.
A further problem was the area required to form these prior bandgap regulators. In order to minimize power dissipation, the size of the resistors had to be increased thereby increasing the cost of the bandgap regulator.
Accordingly, it is desirable to have a bandgap regulator that operates at low currents in order to achieve low power dissipation, that has an accuracy greater than plus or minus four percent (4%), that minimizes leakage current effects, that has an improved power supply rejection ratio, and that does not utilize larger resistor values that consume large amounts of area.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor.